Tetrafluoroethylene copolymers having sulfonyl groups

ABSTRACT

A copolymer having tetrafluoroethylene units and units independently represented by formula (I) in a range from 0.02 to 2 mole percent, based on the total amount of the copolymer. Rf is a linear or branched perfluoroalkyl group having from 1 to 8 carbon atoms and optionally interrupted by one or more —O— groups, each n is independently from 1 to 6, m is 0 or 1, and z is 0, 1, or 2. The copolymer has a melt flow index in a range from 20 grams per 10 minutes to 40 grams per 10 minutes and has in a range from 2 to 200 —SO 2 X groups per 10 6  carbon atoms and up to 100 unstable end groups per 10 6  carbon atoms. The copolymer can be extruded to make articles, such as insulated cables. A method of making the copolymer is also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage filing under 35 U.S.C. 371 ofPCT/US2016/017709, filed Feb. 12, 2016, which claims priority to U.S.Provisional Application Nos. 62/115,462; 62/115,470; and 62/115,476,filed Feb. 12, 2015, the disclosures of which are incorporated byreference in their entirety herein.

BACKGROUND

Melt processable copolymers of tetrafluoroethylene (TFE) andhexafluoropropylene (HFP), known under the name FEP (that is,fluorinated ethylene propylene copolymer), have useful properties suchas chemical resistance, weather resistance, low flammability, thermalstability, and excellent electrical properties. Such beneficialproperties render these fluoropolymers useful, for example, in articlessuch as tubes, pipes, foils, and films. Various embodiments of FEPcopolymers have been reported useful as coatings for wires and cables.See, for example, U.S. Pat. Nos. 5,677,404 and 5,703,185, each to Blair;U.S. Pat. No. 6,541,588 (Kaulbach); U.S. Pat. Nos. 6,743,508 and7,923,519, each to Kono; and U.S. Pat. Nos. 7,122,609 and 7,126,056,each to Earnest. Certain TFE and FEP copolymers have been reported to beuseful as polymer processing additives. See, for example, U.S. Pat. No.5,089,200 (Chapman et al.) and U.S. Pat. No. 5,010,130 (Chapman et al.).

Using perfluoroalkoxyalkyl vinyl ethers as comonomers withtetrafluoroethylene has been reported in U.S. Pat. No. 7,060,772(Hintzer).

SUMMARY

The present disclosure provides tetrafluoroethylene (TFE) copolymersuseful, for example, for wire coating. With a melt flow index (MFI) of30±10, the copolymer can typically be extruded at high speed. With anumber of sulfonyl groups in a range from 2 to 200 per 10⁶ carbon atomsand a number of unstable end groups up to 100 per 10⁶ carbon atoms, abalance of excellent adhesion to metal and thermal stability useful forhigh-temperature and high-speed extrusion can be achieved.

In one aspect, the present disclosure provides a copolymer havingtetrafluoroethylene units and units independently represented by formula

in a range from 0.02 to 2 mole percent, based on the total amount of thecopolymer. Rf is a linear or branched perfluoroalkyl group having from 1to 8 carbon atoms and optionally interrupted by one or more —O— groups,m is 0 or 1, each n is independently from 1 to 6, and z is 0, 1, or 2.The copolymer has a melt flow index in a range from 20 grams per 10minutes to 40 grams per 10 minutes and has in a range from 2 to 200—SO₂X groups per 10⁶ carbon atoms and up to 100 unstable end groups per10⁶ carbon atoms. In the SO₂X groups, X is independently —F, —NH₂, —OH,or —OZ, wherein Z is independently a metallic cation or a quaternaryammonium cation. The unstable end groups typically comprise at least oneof —COOM, —CH₂OH, —COF, and —CONH₂, wherein M is independently an alkylgroup, a hydrogen atom, a metallic cation, or a quaternary ammoniumcation. In some embodiments, the copolymer includes units derived fromperfluorinated terminal olefin having from 3 to 8 carbon atoms. The SO₂Xgroups may be pendant from the polymer chain or may be end groups.

In another aspect, the present disclosure provides a method of making anextruded article. The method includes extruding a melted compositionthat includes the copolymer described above. In some embodiments, themelted composition consists of the copolymer described above. In someembodiments, the extruded article is a film, tube, pipe, or hose. Insome embodiments, the melted composition is extruded onto a conductor.In some embodiments, the melted composition is extruded onto a cable.

In another aspect, the present disclosure provides an extruded articlethat includes the copolymer described above. In some embodiments, theextruded article is a film, tube, pipe, or hose. In some embodiments,the extruded article is a conductor having the copolymer extruded on it.In some embodiments, the extruded article is a cable having thecopolymer extruded on it.

In another aspect, the present disclosure provides a method of makingthe copolymer described above. The method includes copolymerizingcomponents that include tetrafluoroethylene and at least one compoundindependently represented by formulaCF₂═CF(CF₂)_(m)(OC_(n)F_(2n))_(z)ORf. Rf is a linear or branchedperfluoroalkyl group having from 1 to 8 carbon atoms and optionallyinterrupted by one or more —O— groups, m is 0 or 1, each n isindependently from 1 to 6, and z is 0, 1, or 2. Copolymerizing may becarried out, for example, by aqueous emulsion polymerization orsuspension polymerization. In some embodiments, the components includeat least one perfluorinated terminal olefin independently having from 3to 8 carbon atoms.

In embodiments in which the fluoropolymer is in contact with a metal,the SO₂X groups in the copolymers disclosed herein can provide excellentadhesion to metal. The SO₂X groups in the copolymers disclosed hereinare more stable than —COOM, —CH₂OH, —COF, and —CONH₂, referred to hereinas unstable end groups. Thus, SO₂X groups do not cause discoloration,which is typically observed when polymers having unstable end groups areprocessed. Furthermore, post-fluorination is useful for eliminatingunstable end groups without removing the SO₂X groups in the copolymersdisclosed herein.

In this application:

Terms such as “a”, “an” and “the” are not intended to refer to only asingular entity, but include the general class of which a specificexample may be used for illustration. The terms “a”, “an”, and “the” areused interchangeably with the term “at least one”.

The phrase “comprises at least one of” followed by a list refers tocomprising any one of the items in the list and any combination of twoor more items in the list. The phrase “at least one of” followed by alist refers to any one of the items in the list or any combination oftwo or more items in the list.

The terms “perfluoro” and “perfluorinated” refer to groups in which allC—H bonds are replaced by C—F bonds.

The phrase “interrupted by at least one —O— group”, for example, withregard to a perfluoroalkyl or perfluoroalkylene group refers to havingpart of the perfluoroalkyl or perfluoroalkylene on both sides of the —O—group. For example, —CF₂CF₂—O—CF₂—CF₂— is a perfluoroalkylene groupinterrupted by an —O—.

All numerical ranges are inclusive of their endpoints and nonintegralvalues between the endpoints unless otherwise stated (e.g., 1 to 5includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.).

DETAILED DESCRIPTION

The copolymer according to the present disclosure may be useful for avariety of applications. For example, copolymers according to thepresent disclosure are useful for insulating cable or wire. Suchinsulated cable may be useful, for example, as a communication cable(e.g., a data transmission cable such as a “Local Area Network” (LAN)cable). In general, the insulated cable can be manufactured by extrusioncoating molten copolymer in the shape of a tube and then drawing downthe copolymer by inserting a core wire through the center portion of theresin tube in its axial direction. The term “draw-down” as used hereinmeans extending a molten resin extruded from a die having an opening ofrelatively large sectional area to its final intended dimensions. Thedraw-down is characterized by a draw-down ratio (DDR), which is theratio of the sectional area of the opening of the die to the sectionalarea of the insulated material of the final product. In general, thedraw-down ratio is suitably from 50 to 150.

The copolymer according to the present disclosure includestetrafluoroethylene units copolymerized with units independentlyrepresented by formula:

in which m is 0 or 1, each n is independently from 1 to 6, z is 0, 1, or2, and Rf is a linear or branched perfluoroalkyl group having from 1 to8 carbon atoms and optionally interrupted by one or more —O— groups. Insome embodiments, m is 0, and z is 1. In some of these embodiments, n isfrom 1 to 4, or from 1 to 3, or from 2 to 3, or from 2 to 4. In someembodiments, n is 1 or 3. In some embodiments, n is 3. When z is 2, then in the two C_(n)F_(2n) groups may be independently selected. However,within a C_(n)F_(2n) group, a person skilled in the art would understandthat n is not independently selected. C_(n)F_(2n) may be linear orbranched. In some embodiments, C_(n)F_(2n) can be written as (CF₂)_(n),which refers to a linear perfluoroalkylene group. In some embodiments,C_(n)F_(2n) is —CF₂—CF₂—CF₂—. In some embodiments, C_(n)F_(2n) isbranched, for example, —CF₂—CF(CF₃)—. In some embodiments,(OC_(n)F_(2n))_(z) is represented by —O—(CF₂)₁₋₄—[O(CF₂)₁₋₄]₀₋₁. In someembodiments, Rf is a linear or branched perfluoroalkyl group having from1 to 8 (or 1 to 6) carbon atoms that is optionally interrupted by up to4, 3, or 2 —O— groups. In some embodiments, Rf is a perfluoroalkyl grouphaving from 1 to 4 carbon atoms optionally interrupted by one —O— group.In embodiments in which m is 0 and z is 1 or 2, copolymers are preparedby copolymerizing components including tetrafluoroethylene and at leastone perfluoroalkoxyalkyl vinyl ether independently represented byformula CF₂═CF(OC_(n)F_(2n))_(z)ORf, in which n and Rf are as definedabove in any of their embodiments. Examples of suitableperfluoroalkoxyalkyl vinyl ethers include CF₂═CFOCF₂OCF₃,CF₂═CFOCF₂OCF₂CF₃, CF₂═CFOCF₂CF₂OCF₃, CF₂═CFOCF₂CF₂CF₂OCF₃,CF₂═CFOCF₂CF₂CF₂CF₂OCF₃, CF₂═CFOCF₂CF₂OCF₂CF₃, CF₂═CFOCF₂CF₂CF₂OCF₂CF₃,CF₂═CFOCF₂CF₂CF₂CF₂OCF₂CF₃, CF₂═CFOCF₂CF₂OCF₂OCF₃,CF₂═CFOCF₂CF₂OCF₂CF₂OCF₃, CF₂═CFOCF₂CF₂OCF₂CF₂CF₂OCF₃,CF₂═CFOCF₂CF₂OCF₂CF₂CF₂CF₂OCF₃, CF₂═CFOCF₂CF₂OCF₂CF₂CF₂CF₂CF₂OCF₃,CF₂═CFOCF₂CF₂(OCF₂)₃OCF₃, CF₂═CFOCF₂CF₂(OCF₂)₄OCF₃,CF₂═CFOCF₂CF₂OCF₂OCF₂OCF₃, CF₂═CFOCF₂CF₂OCF₂CF₂CF₃,CF₂═CFOCF₂CF₂OCF₂CF₂OCF₂CF₂CF₃, CF₂═CFOCF₂CF(CF₃)—O—C₃F₇ (PPVE-2),CF₂═CF(OCF₂CF(CF₃))₂—O—C₃F₇ (PPVE-3), and CF₂═CF(OCF₂CF(CF₃))₃—O—C₃F₇(PPVE-4). Many of these perfluoroalkoxyalkyl vinyl ethers can beprepared according to the methods described in U.S. Pat. No. 6,255,536(Worm et al.) and U.S. Pat. No. 6,294,627 (Worm et al.). It should beunderstood that for embodiments in which m is 0 and z is 1, the unitscopolymerized with tetrafluoroethylene units are represented by formula:

In some embodiments of the copolymer according to the presentdisclosure, m is 1, z is 1, and n and Rf are as defined above in any oftheir embodiments. In embodiments in which m is 1 and z is 1 or 2,copolymers are prepared by copolymerizing components includingtetrafluoroethylene and at least one perfluoroalkoxyalkyl allyl etherindependently represented by formula CF₂═CFCF₂(OC_(n)F_(2n))_(z)ORf, inwhich n and Rf are as defined above in any of their embodiments.Examples of suitable perfluoroalkoxyalkyl allyl ethers includeCF₂═CFCF₂OCF₂CF₂OCF₃, CF₂═CFCF₂OCF₂CF₂CF₂OCF₃, CF₂═CFCF₂OCF₂OCF₃,CF₂═CFCF₂OCF₂OCF₂CF₃, CF₂═CFCF₂OCF₂CF₂CF₂CF₂OCF₃,CF₂═CFCF₂OCF₂CF₂OCF₂CF₃, CF₂═CFCF₂OCF₂CF₂CF₂OCF₂CF₃,CF₂═CFCF₂OCF₂CF₂CF₂CF₂OCF₂CF₃, CF₂═CFCF₂OCF₂CF₂OCF₂OCF₃,CF₂═CFCF₂OCF₂CF₂OCF₂CF₂OCF₃, CF₂═CFCF₂OCF₂CF₂OCF₂CF₂CF₂OCF₃,CF₂═CFCF₂OCF₂CF₂OCF₂CF₂CF₂CF₂OCF₃, CF₂═CFCF₂OCF₂CF₂OCF₂CF₂CF₂CF₂CF₂OCF₃,CF₂═CFCF₂OCF₂CF₂(OCF₂)₃OCF₃, CF₂═CFCF₂OCF₂CF₂(OCF₂)₄OCF₃,CF₂═CFCF₂OCF₂CF₂OCF₂OCF₂OCF₃, CF₂═CFCF₂OCF₂CF₂OCF₂CF₂CF₃,CF₂═CFCF₂OCF₂CF₂OCF₂CF₂OCF₂CF₂CF₃, CF₂═CFCF₂OCF₂CF(CF₃)—O—C₃F₇, andCF₂═CFCF₂(OCF₂CF(CF₃))₂—O—C₃F₇. Many of these perfluoroalkoxyalkyl allylethers can be prepared, for example, according to the methods describedin U.S. Pat. No. 4,349,650 (Krespan).

In some embodiments of the copolymer according to the presentdisclosure, m and z are each 0. It should be understood that when m andz are each 0, the units copolymerized with tetrafluoroethylene units arerepresented by formula:

in which Rf is a linear or branched perfluoroalkyl group having from 1to 8 carbon atoms optionally interrupted by one or more —O— groups. Insome of these embodiments, Rf is a linear or branched perfluoroalkylgroup having from 1 to 8 carbon atoms (that is, not interrupted by oneor more —O— groups). In some embodiments, Rf is a linear or branchedperfluoroalkyl group having from 1 to 6, 1 to 5, 1 to 4, or 1 to 3carbon atoms. These units are typically incorporated into the copolymerby including perfluoroalkyl vinyl ethers [e.g., perfluoromethyl vinylether (CF₂═CFOCF₃), perfluoroethyl vinyl ether (CF₂═CFOCF₂CF₃), andperfluoropropyl vinyl ether (CF₂═CFOCF₂CF₂CF₃)] in the components thatare copolymerized. In other embodiments, the copolymers according to thepresent disclosure are substantially free of such perfluoroalkyl vinylether-derived units. For example, the copolymer can include up to 0.02,0.01, or 0.005 mole percent of such perfluoroalkyl vinyl ether-derivedunits. The term “substantially free of” also includes copolymers thatinclude none of these perfluoroalkyl vinyl ether-derived units.

In some embodiments of the copolymer according to the presentdisclosure, m is 1, z is 0, and Rf is as defined above in any of itsembodiments. In these embodiments, copolymers according to the presentdisclosure can be prepared by copolymerizing components includingtetrafluoroethylene and at least one perfluoroalkyl allyl etherindependently represented by formula CF₂═CFCF₂ORf, in which Rf is asdefined above in any of its embodiments. Examples of suitableperfluoroalkyl allyl ethers include CF₂═CF—CF₂—O—CF₃,CF₂═CF₂—CF₂—O—C₂F₅, and CF₂═CF—CF₂—O—C₃F₇.

The copolymerized units independently represented by formula:

are present in the copolymer according to the present disclosure in arange from 0.02 mole percent to 2 mole percent, based on the totalamount of the copolymer. In some embodiments, the copolymerized unitsrepresented by this formula are present in the copolymer in an amount upto 1.5 mole percent or up to 1.0 mole percent. In some embodiments, thecopolymerized units represented by this formula are present in thecopolymer in an amount of at least 0.03 mole percent or 0.05 molepercent. The copolymerized units may be present in the copolymer in arange from 0.02 mole percent to 2 mole percent, 0.03 mole percent to 1.5mole percent, or 0.05 mole percent to 1.0 mole percent. Copolymersaccording to the present disclosure may include any combination of oneor more of these copolymerized units according to any of the aboveembodiments.

The copolymer according to the present disclosure has in a range from 2to 200 —SO₂X groups per 10⁶ carbon atoms. In the —SO₂X groups, X isindependently —F, —NH₂, —OH, or —OZ, wherein Z is independently ametallic cation (e.g., an alkali-metal cation such as sodium orpotassium) or a quaternary ammonium cation (e.g., tetraalkyl ammonium,wherein alkyl has from 1 to 4, 1 to 3, or 1 to 2 carbon atoms). In someembodiments, X is independently —F, —OH or —OZ. In some embodiments, Xis independently —OH or —OZ. In some of these embodiments, Z is a metalcation (e.g., an alkali-metal cation such as sodium or potassium). The—SO₂X groups may be present in copolymerized units of the copolymer, atthe ends of copolymer chains, or a combination thereof.

In some embodiments, the copolymer according to the present disclosureincludes copolymerized units comprising the —SO₂X groups. In some ofthese embodiments, the copolymer further comprises units represented byformula

wherein a is 0 or 1, each b is independently from 1 to 4, c is 0 to 4, dis 0 or 1, e is 1 to 6, and X is as defined above in any of itsembodiments. In some embodiments, b is 1 to 3, 1 to 2, or 1. In someembodiments, c is 0, 1, or 2; 1 or 2; or 0 or 1. In some embodiments, eis 1 to 4, 1 to 3, or 1 to 2. In some embodiments, c is 0, d is 1, and eis 1 to 4. In some embodiments, a is 0, OC_(b)F_(2b) is OCF₂CF(CF₃), cis 1 or 2, d is 1, and e is 1 to 4. In some embodiments, a is 1, b is 1,c is 0 to 4, d is 1, e is 1 to 4. C_(e)F_(2e) may be linear or branched.In some embodiments, C_(e)F_(2e) can be written as (CF₂)_(e), whichrefers to a linear perfluoroalkylene group. When c is 2, the b in thetwo C_(b)F_(2b) groups may be independently selected. However, within aC_(b)F_(2b) group, a person skilled in the art would understand that bis not independently selected.

These units comprising —SO₂X groups may be incorporated into thecopolymer by including one or more olefin monomers independentlyrepresented by formulaCF₂═CF(CF₂)a—(OC_(b)F_(2b))_(c)—(O)_(d)—(C_(e)F_(2e))—SO₂X, wherein a,b, c, d, e, and X are as defined above, in the components that arecopolymerized. Examples of suitable olefin monomers represented byformula CF₂CF(CF₂)_(a)—(OC_(b)F_(2b))_(c)—(O)_(d)—(C_(e)F_(2e))—SO₂Xinclude CF₂═CF—CF₂—SO₂X, CF₂═CF—O—CF₂—CF₂—SO₂X,CF₂═CF—CF₂—O—CF₂—CF₂—SO₂X, CF₂═CF—O—(CF₂)₄—SO₂X,CF₂═CF—CF₂—O—(CF₂)₄—SO₂X, and CF₂═CF—O—CF₂—CF(CF₃)—O—CF₂—CF₂—SO₂X.Certain of these olefin monomers are commercially available. Others maybe prepared by known methods. See, for example, U.S. Pat. No. 3,282,875(Connolly), U.S. Pat. No. 3,718,627 (Grot), U.S. Pat. No. 4,267,364(Grot), and U.S. Pat. No. 4,273,729 (Krespan). To achieve a range from 2to 200 —SO₂X groups per 10⁶ carbon atoms, the amount of these olefinmonomers is typically less than 1.0 weight percent (wt. %), in someembodiments, less than 0.6 wt. %, based on the total weight of themonomers incorporated into the copolymer. To achieve a range from 0 to200 —SO₂X groups per 10⁶ carbon atoms, the amount ofCF₂═CF—O—CF₂—CF(CF₃)—O—CF₂—CF₂—SO₂X, for example, is typically less than0.18 wt. %, based on the total weight of the monomers incorporated intothe copolymer.

In some embodiments, the copolymer according to the present disclosurecomprises a copolymer of tetrafluoroethylene (TFE), units independentlyrepresented by formula

and units derived from one or more perfluorinated terminal olefinsindependently having from 3 to 8 carbon atoms. In some embodiments, theperfluorinated terminal olefin units independently have from 3 to 7, 3to 6, 3 to 5, or 3 to 4 carbon atoms. In some embodiments, theperfluorinated terminal olefins providing these units comprise at leastone of CF₂═CF—CF₃ or CF₂═CF—C₂F₅. In some embodiments, theperfluorinated terminal olefin units are hexafluoropropylene (HFP)units. The copolymers according to the present disclosure are at leastpartially crystalline fluoroplastics. A person skilled in the art canselect the amount of perfluorinated terminal olefins to include in thepolymerization to make an at least partially crystalline fluoroplastic.In some embodiments, the perfluorinated terminal olefin units may bepresent in a range from 5 weight percent (wt. %) to 22 wt. %, in a rangefrom 10 wt. % to 17 wt. %, or in a range from 11 wt. % to 16 wt. %,based on the total weight of the copolymer.

In some embodiments, the copolymer according to the present disclosurecomprises a copolymer of TFE, HFP, and units independently representedby formula

The HFP may be present in a range from 5 wt. % to 22 wt. %, in a rangefrom 10 wt. % to 17 wt. %, in a range from 11 wt. % to 16 wt. %, or in arange from 11.5 wt. % to 15.8 wt. %, based on the total weight of TFEand HFP.

The copolymers according to the present disclosure typically have amelting point between 220° C. to 285° C., in some embodiments, 235° C.to 275° C., 240° C. to 275° C., or 245° C. to 265° C.

The molecular weights of certain fluoroplastics are often characterizedby the melt viscosity or the melt flow index (MFI; e.g., 372° C./5 kg)).The copolymer according to the present disclosure has an MFI of 30±10grams per 10 minutes. In some embodiments, the copolymer according tothe present disclosure has an MFI of 30±5 grams per 10 minutes or 30±3grams per 10 minutes. When the MFI is 30±10 grams per 10 minutes,high-speed extrusion is possible, the extruded polymer can be readilydrawn down, and melt fracture (that is, abnormal flow and surfaceroughness of the extruded polymer) is minimized. If the MFI is less than20 grams per 10 minutes, high extrusion rates are difficult to achieve.Also, an FEP having an MFI of up to about 40 typically performs betterunder cable burn performance evaluation than FEP copolymers with higherMFIs due to a lower tendency to flow at high temperature. The copolymeraccording to the present disclosure can be adjusted to have an MFI of30±10 grams per 10 minutes by adjusting the amount of the initiatorand/or chain-transfer agent used during polymerization, both of whichaffect the molecular weight and molecular-weight distribution of thecopolymer. MFI can also be controlled by the rate of addition ofinitiator to the polymerization. Variations in the monomer compositioncan also affect the MFI. For the purposes of the present disclosure, MFIis measured according to the test method described in the Examples,below.

At a given MFI, even relatively low levels of a comonomer having aperfluorinated ether pendant group as described herein can improve theproperties of a TFE-containing copolymer. For example, even at lowlevels, a comonomer having a perfluorinated ether pendant group mayincrease the elongation viscosity of an FEP copolymer and may have apositive effect on the rupture durability and cable burn performance ofthe FEP copolymer.

The production of foamed insulation cable is different from thehigh-line-speed production of solid wire insulation, and lower MFIs areuseful in the production of foamed insulation cable. Thus, in someembodiments, the copolymer according to the present disclosure is notfoamed. In these embodiments, the copolymer generally does not include afoam cell nucleating agent (e.g., a F(CF₂)CH₂CH₂-sulfonic or phosphonicacid or salt, wherein x is 6, 8, 10, or 12 or a mixture thereof that mayor may not be combined with boron nitride). Likewise, in someembodiments of the extruded article according to and/or made accordingto the present disclosure, the extruded article is not foamed or doesnot include a foam cell nucleating agent. In some of these embodiments,the extruded article is not a foamed insulation cable.

However, it may be desirable in some applications for the copolymeraccording to the present disclosure to be foamed. In these embodiments,the copolymer can include a foam cell nucleating agent as describedabove. Likewise, in some embodiments of the extruded article accordingto and/or made according to the present disclosure, the extruded articleis foamed or includes a foam cell nucleating agent. In some of theseembodiments, the extruded article is a foamed insulation cable.

It has been reported in U.S. Pat. No. 4,552,925 (Nakagawa et al.), forexample, that high extrusion speed can be achieved for FEP copolymerswhen the molecular-weight distribution of the copolymer is very broad.To achieve a broad molecular-weight distribution, a mixture of at leasttwo FEP copolymers with largely differing molecular weights (as measuredby MFI, for example) can be used. The desired mixtures are oftenproduced by polymerizing the components separately and mixing them inform of the latices, reactor beads, or fluff before melt pelletizing.Thus, the manufacturing of these mixtures is a cumbersome and costlyprocess.

In contrast, in some embodiments, the copolymer according to the presentdisclosure has a relatively low polydispersity. The polydispersity,which is a ratio of the weight-average molecular weight (Mw) to thenumber-average molecular weight (Mn) of the copolymer, can be up toabout 2.5, 2.3, 2.2, or 2.0. The polydispersity may be as low as 1.5.Polydispersity is measured according to a modified version of the methodpublished by W. H. Tuminello in Polym. Eng. Sci. 26, 1339 (1986),described in the Examples, below.

Copolymers according to the present disclosure can be prepared in avariety of ways. Conveniently, the method of making the copolymeraccording to the present disclosure includes radical aqueous emulsionpolymerization.

When conducting emulsion polymerization, perfluorinated or partiallyfluorinated emulsifiers may be useful. Generally these fluorinatedemulsifiers are present in a range from about 0.02% to about 3% byweight with respect to the polymer. Polymer particles produced with afluorinated emulsifier typically have an average diameter, as determinedby dynamic light scattering techniques, in range of about 10 nanometers(nm) to about 300 nm, and in some embodiments in range of about 50 nm toabout 200 nm. Examples of suitable emulsifiers include perfluorinatedand partially fluorinated emulsifier having the formula[R_(f)—O-L-COO⁻]_(i)X^(i+) wherein L represents a linear partially orfully fluorinated alkylene group or an aliphatic hydrocarbon group,R_(f) represents a linear partially or fully fluorinated aliphatic groupor a linear partially or fully fluorinated aliphatic group interruptedwith one or more oxygen atoms, X^(i+) represents a cation having thevalence i and i is 1, 2 or 3. (See, e.g., U.S. Pat. No. 7,671,112 toHintzer et al.). Additional examples of suitable emulsifiers alsoinclude perfluorinated polyether emulsifiers having the formulaCF₃—(OCF₂)_(x)—O—CF₂X, wherein x has a value of 1 to 6 and X representsa carboxylic acid group or salt thereof, and the formulaCF₃—O—(CF₂)₃—(OCF(CF₃)—CF₂)_(y)—O-L-Y wherein y has a value of 0, 1, 2or 3, L represents a divalent linking group selected from —CF(CF₃)—,—CF₂—, and —CF₂CF₂—, and Y represents a carboxylic acid group or saltthereof (See, e.g., U.S. Pat. Publ. No. 2007/0015865 to Hintzer et al.).Other suitable emulsifiers include perfluorinated polyether emulsifiershaving the formula R_(f)O(CF₂CF₂O)_(x)CF₂COOA wherein R_(f) isC_(b)F_((2b+1)); where b is 1 to 4, A is a hydrogen atom, an alkalimetal or NH₄, and x is an integer of from 1 to 3. (See, e.g., U.S. Pat.Publ. No. 2006/0199898 to Funaki et al.). Suitable emulsifiers alsoinclude perfluorinated emulsifiers having the formulaF(CF₂)_(b)O(CF₂CF₂O)CF₂COOA wherein A is a hydrogen atom, an alkalimetal or NH₄, b is an integer of from 3 to 10, and x is 0 or an integerof from 1 to 3. (See, e.g., U.S. Pat. Publ. No. 2007/0117915 to Funakiet al.). Further suitable emulsifiers include fluorinated polyetheremulsifiers as described in U.S. Pat. No. 6,429,258 to Morgan et al. andperfluorinated or partially fluorinated alkoxy acids and salts thereofwherein the perfluoroalkyl component of the perfluoroalkoxy has 4 to 12carbon atoms, or 7 to 12 carbon atoms. (See, e.g., U.S. Pat. No.4,621,116 to Morgan). Suitable emulsifiers also include partiallyfluorinated polyether emulsifiers having the formula[R_(f)—(O)_(t)—CHF—(CF₂)_(x)—COO-]_(i)X^(i+) wherein R_(f) represents apartially or fully fluorinated aliphatic group optionally interruptedwith one or more oxygen atoms, t is 0 or 1 and x is 0 or 1, X^(i+)represents a cation having a valence i and i is 1, 2 or 3. (See, e.g.,U.S. Pat. Publ. No. 2007/0142541 to Hintzer et al.). Further suitableemulsifiers include perfluorinated or partially fluorinatedether-containing emulsifiers as described in U.S. Pat. Publ. Nos.2006/0223924, 2007/0060699, and 2007/0142513 each to Tsuda et al. and2006/0281946 to Morita et al. Fluoroalkyl, for example, perfluoroalkylcarboxylic acids and salts thereof having 6-20 carbon atoms, such asammonium perfluorooctanoate (APFO) and ammonium perfluorononanoate (see,e.g., U.S. Pat. No. 2,559,752 to Berry) may also be useful.

If desired, the emulsifiers can be removed or recycled from thefluoropolymer latex as described in U.S. Pat. No. 5,442,097 to Obermeieret al., U.S. Pat. No. 6,613,941 to Felix et al., U.S. Pat. No. 6,794,550to Hintzer et al., U.S. Pat. No. 6,706,193 to Burkard et al., and U.S.Pat. No. 7,018,541 to Hintzer et al.

In some embodiments of the method of making the copolymer according tothe present disclosure, the polymerization process may be conducted withno emulsifier or with no fluorinated emulsifier.

In some embodiments of the method of making the copolymer according tothe present disclosure, a water-soluble initiator can be useful to startthe polymerization process. Salts of peroxy sulfuric acid, such asammonium persulfate or potassium persulfate, are typically appliedeither alone or sometimes in the presence of a reducing agent, such asbisulfites or sulfinates (e.g., fluorinated sulfinates disclosed in U.S.Pat. Nos. 5,285,002 and 5,378,782, both to Grootaert) or the sodium saltof hydroxy methane sulfinic acid (sold under the trade designation“RONGALIT”, BASF Chemical Company, New Jersey, USA). The choice ofinitiator and reducing agent, if present, will affect the end groups ofthe copolymer. The concentration range for the initiators and reducingagent can vary from 0.01% to 5% by weight based on the aqueouspolymerization medium.

In some embodiments, at least some of the —SO₂X groups present in thecopolymers according to the present disclosure are introduced bygenerating SO₃ ⁻ radicals during the polymerization process. When saltsof peroxy sulfuric acid are used in the presence of a sulfite orbisulfite salt (e.g., sodium sulfite or potassium sulfite), SO₃ ⁻radicals are generated during the polymerization process, resulting in—SO₃ ⁻ end groups. By altering the stoichiometry of the sulfite orbisulfite salt versus the peroxy sulfuric acid salt, one can vary theamount of —SO₂X end groups.

Most of the initiators and emulsifiers described above have an optimumpH-range where they show most efficiency. For this reason, buffers aresometimes useful. Buffers include phosphate, acetate, or carbonate(e.g., (NH₄)₂CO₃ or NaHCO₃) buffers or any other acid or base, such asammonia or alkali-metal hydroxides. The concentration range for thebuffers can vary from 0.01% to 5% by weight based on the aqueouspolymerization medium.

In some embodiments, the copolymers according to the present disclosuremay include up to 100 ppm, 150 ppm, or more alkali-metal cations oralkaline-earth-metal cations. When alkali-metal salts or bases are usedas initiators or buffers, for example, the copolymer according to thepresent disclosure generally comprises at least 50 ppm alkali-metalcations. In other embodiments of the method of making the copolymeraccording to the present disclosure, polymerization is conducted in theabsence of added alkali-metal cations. In these embodiments, potassiumpersulfate, a common alternative initiator or co-initiator with ammoniumpersulfate, is not used. It is also possible to use organic initiatorsas disclosed in U.S. Pat. No. 5,182,342 (Feiring et al.). The copolymerproduced can have less than 50 ppm alkali-metal cations, in someembodiments, less than 25 ppm, less than 10 ppm, or less than 5 ppmalkali-metal cations. To achieve such low alkali-metal content, thewater for polymerization and washing may be deionized. Minimizing thealkali-metal salt concentration in the copolymer may minimize theformation of die drool that may form during a high speed conductorcoating operation on the outer surface of an extrusion die or on theguider tip inside the die. This die drool, if not minimized, can beperiodically carried along the melt and/or conductor to form undesirablelumps and may cause cone-breaks.

The alkali-metal ion content of the copolymer can be measured by flameatomic absorption spectrometry after combusting the copolymer anddissolving the residue in an acidic aqueous solution according to themethod described in the Examples, below. For potassium as the analyte,the lower detection limit is less than 1 ppm.

Typical chain-transfer agents like H₂, lower alkanes, alcohols, ethers,esters, and methylene fluoride may be useful in the preparation of thecopolymer according to the present disclosure. Termination primarily viachain transfer results in a polydispersity of about 2 or less. In someembodiments of the method according to the present disclosure, thepolymerization is carried out without any chain-transfer agents. A lowerpolydispersity can sometimes be achieved in the absence ofchain-transfer agents. Recombination typically leads to a polydispersityof about 1.5 for small conversions.

Useful polymerization temperatures can range from 40° C. to 120° C.Typically, polymerization is carried out in a temperature range from 40°C. to 100° C. or 50° C. to 80° C. The polymerization pressure is usuallyin the range of 0.8 MPa to 2.5 MPa, and in some embodiments in the rangefrom 1.0 MPa to 2.0 MPa. HFP and other perfluorinated terminal olefinscan be precharged and fed into the reactor as described, for example, inModern Fluoropolymers, ed. John Scheirs, Wiley & Sons, 1997, p. 241.Perfluorinated vinyl or allyl ethers represented by formulaCF₂═CF(CF₂)_(m)(OC_(n)F_(2n))_(z)ORf, wherein m, n, z, and Rf are asdefined above in any of their embodiments, are typically liquids and maybe sprayed into the reactor or added directly, vaporized, or atomized.Perfluorinated vinyl or allyl ethers represented by formulaCF₂═CF(CF₂)_(m)(OC_(n)F_(2n))_(z)ORf may also be pre-emulsified with anemulsifier before being combined with the other comonomers, for example,before addition of a gaseous fluoroolefin.

The obtained polymer dispersion after aqueous emulsion polymerizationcan be used as is or, if higher solids are desired, can beupconcentrated. To coagulate the obtained fluoropolymer latex, anycoagulant which is commonly used for coagulation of a fluoropolymerlatex may be used. The coagulant may be, for example, a water-solublesalt (e.g., calcium chloride, magnesium chloride, aluminum chloride oraluminum nitrate), an acid (e.g., nitric acid, hydrochloric acid orsulfuric acid), or a water-soluble organic liquid (e.g., alcohol oracetone). The amount of the coagulant to be added may be in a range of0.001 to 20 parts by mass, for example, in a range of 0.01 to 10 partsby mass per 100 parts by mass of the fluoropolymer latex. Alternativelyor additionally, the fluoropolymer latex may be frozen for coagulationor mechanically coagulated, for example, with a homogenizer as describedin U.S. Pat. No. 5,463,021 (Beyer et al.). In some embodiments (e.g., inembodiments in which the copolymer comprises less than 50 ppmalkali-metal cation), it is useful to avoid alkali-metal salts ascoagulants. It may also be useful to avoid acids andalkaline-earth-metal salts as coagulants to avoid metal contaminants.

The coagulated copolymer can be collected by filtration and washed withwater. The washing water may, for example, be ion-exchanged water, purewater, or ultrapure water. The amount of the washing water may be from 1to 5 times by mass to the copolymer, whereby the amount of theemulsifier attached to the copolymer can be sufficiently reduced by onewashing.

The coagulated copolymer may be agglomerated to produce the polymer inagglomerate form. Agglomerates are typically free-flowing sphericalbeads with an average size (that is, diameter) of 1 mm to 5 mm. If theagglomerates obtained from agglomerating the coagulated copolymer aretoo small, it may be desirable to compact the agglomerate to produce acompacted agglomerate which will typically have an average size of 1 mmto 10 mm. In some embodiments, the coagulated copolymer is agglomeratedwith a water-immiscible organic liquid like gasoline as described inModern Fluoropolymers, ed. by John Scheirs, Wiley & Sons, 1997, p. 227.The agglomerate can be dried, for example, by heating under moderatevacuum at temperatures up to 250° C., 200° C., 180° C., 150° C., or 130°C.

In some embodiments of the method of making the copolymer according tothe present disclosure, radical polymerization also can be carried outby suspension polymerization. Suspension polymerization will typicallyproduce particle sizes up to several millimeters.

In some embodiments, the copolymer may be melted, extruded, and cut intogranulates of a desired size, which may be called melt granulate.

Unstable end groups in the copolymers according to the presentdisclosure include —COOM, —CH₂OH, —COF, and —CONH₂, wherein M isindependently an alkyl group, a hydrogen atom, a metallic cation, or aquaternary ammonium cation. In some embodiments, the unstable end groupsare —COOM and —COF groups. Tetrafluoroethylene copolymers obtained byaqueous emulsion polymerization with inorganic initiators (e.g.persulfates, KMnO₄, etc.) typically have a high number of unstablecarbon-based end groups (e.g. more than 200 —COOM end groups per 10⁶carbon atoms). During work-up and melt-pelletizing of thetetrafluoroethylene copolymers, the copolymers take on a brownishappearance due to thermal degradation. In these cases, the number ofunstable end groups may be unacceptable for further high-speedprocessing. Accordingly, the copolymers according to the presentdisclosure have up to 100 unstable end groups per 10⁶ carbon atoms. Insome embodiments, the copolymers according to the present disclosurehave up to 75, 50, 40, 30, 25, 20, 15, or 10 unstable end groups per 10⁶carbon atoms. The number of unstable end groups can be determined byFourier-transform infrared spectroscopy, as described in the Examples,below.

The mechanism of the degradation of thermally unstable end groups hasbeen described in some detail in Modern Fluoropolymers, John Wiley &Sons, 1997, in K. Hintzer and G. Lohr, ‘Melt ProcessableTetrafluoroethylene-Perfluoropropylvinyl Ether Copolymers (PFA)’, page227f. During the thermal degradation, corrosive gases are produced andconsiderably impair the quality of the final product via metalcontamination or bubble formation, and can corrode tooling andprocessing machinery. The effect naturally increases as molecular weightdecreases and melt flow index increases.

While the copolymer according to the present disclosure has relativelyfew unstable end groups, it is desirable to have a certain amount ofpolar groups to ensure good adhesion of the polymer to metal surfaces(e.g. copper wires). We have found that copolymers according to thepresent disclosure, which have stable polar —SO₂X groups, ensure goodadhesion to metal surfaces. These copolymers typically have a brilliantcolor and do not exhibit the brownish appearance that can occur whenCOOM end groups thermally degrade. The copolymer according to thepresent disclosure has in a range from 2 to 200 —SO₂X groups per 10⁶carbon atoms, wherein X is as defined above in any of its embodiments.In some embodiments, the copolymer according to the present disclosurehas at least 5, 10, 15, 20, 25, 30, 35, 40, or 50 —SO₂X end groups per10⁶ carbon atoms.

Various treatments of molten or unmolten fluoropolymer have beenproposed to reduce the amount of unstable end groups, resulting insubstantial suppression of thermal degradation. When the unstable endgroups are acid end groups, —COF or —COOH, the fluoropolymer can betreated with ammonia to form the more stable amide end group —CONH₂ orwith a primary or secondary amine (e.g., dimethyl, diethyl, or propylamine) to form amide end groups —CONRH or —CONR₂, wherein R is/are thealkyl group(s) of the amine, and wherein for R₂, the alkyl groups arethe same or different. When the unstable end groups are acid end groups,—COF or —COOH, the fluoropolymer can be treated with an alcohol, such asmethanol, ethanol, propanol, or a fluorine-containing alcohol to formthe more stable ester —COOR′ where R′ is the alkyl group supplied by thealcohol. When the unstable end groups are —COF or —COOM, thefluoropolymer can be decarboxylated to form the more stable —CF₂H and—CF(CF₃)H end groups, respectively. Treatment of fluoropolymers at hightemperatures (e.g., 400° C.) with water vapor has been shown to reducethe number of unstable end groups, typically forming CF₂H and —CF(CF₃)Hend groups. See, e.g., U.S. Pat. No. 3,085,083 (Schreyer). The method ofmaking the copolymer according to the present disclosure can include anyof these methods.

Post-fluorination with fluorine gas is also commonly used to cope withunstable end groups and any concomitant discoloration. Post-fluorinationtypically results in a melt pelletized copolymer with an excellentcolor, and the number of unstable end groups is reduced almost to zero.Post-fluorination of the fluoropolymer can convert —COOH, amide,hydride, —COF, and other non-perfluorinated end groups or —CF═CF₂ to—CF₃ end groups. Converting the thermally unstable end groups intostable —CF₃ end groups by post-fluorination of agglomerate or meltgranulate has been described, for example, in U.S. Pat. No. 4,743,658(Imbalzano et al.) and Great Britain Patent GB1210794, published Oct.28, 1970. A stationary bed of agglomerate may also be fluorinated asdescribed in U.S. Pat. No. 6,693,164 (Blong).

In some embodiments, the copolymer according to the present disclosurecan be prepared by a method including a post-fluorination step aftermelt-pelletization of the polymer in order to remove unstable,carbon-based end groups (e.g. —COF, COOM, —CONH₂, —CH₂OH). Thepost-fluorination can be conveniently carried out with nitrogen/fluorinegas mixtures in ratios of 80-90:20-10 at temperatures between 20° C. and250° C., in some embodiments in a range of 50° C. to 200° C. or 70° C.to 120° C., and pressures from 1-10 bar. Under these conditions, mostunstable carbon-based end groups are removed, whereas SO₂X groups mostlysurvive.

In some embodiments, the copolymer according to the present disclosurecan be prepared by a method including a post-treatment with aqueousammonia solution after the post-fluorination to obtain —SO₂NH₂ groups, amethod including a post-treatment with aqueous alkaline hydroxide (e.g.LiOH, NaOH, or KOH) solution to obtain SO₃ alkaline-groups orsubsequently SO₃H groups, or a method including post-treatment withwater and steam to form SO₃H groups.

In some embodiments, copolymers according to the present disclosureinclude —CF₂H and/or —CF(CF₃)H end groups. In some embodiments of themethod according to the present disclosure (e.g., when alkali-metalcations are present) the dried polymer contains predominantly —CF₂H and—CF(CF₃)H end groups as described above. —CF₂H and —CF(CF₃)H end groupsare sufficiently stable for some applications. However, ifpost-fluorination is desired to convert some of the —CF₂H and —CF(CF₃)Hend groups into —CF₃ and —C₂F₅ end groups, respectively, thepost-fluorination is generally easier and faster than when many —COOHend groups are present since a lower level of fluorination is needed toconvert the —CF₂H or —CF(CF₃)H end groups in comparison to —COOH endgroups.

Some Embodiments of the Disclosure

In a first embodiment, the present disclosure provides a copolymercomprising tetrafluoroethylene units and units independently representedby formula

in a range from 0.02 to 2 mole percent, based on the total amount of thecopolymer, wherein each n is independently from 1 to 6, m is 0 or 1, zis 0, 1, or 2, and Rf is a linear or branched perfluoroalkyl grouphaving from 1 to 8 carbon atoms and optionally interrupted by one ormore —O— groups, wherein the copolymer has a melt flow index in a rangefrom 20 grams per 10 minutes to 40 grams per 10 minutes measured at atemperature of 372° C. and at a support weight of 5.0 kg, wherein thecopolymer has in a range from 2 to 200 —SO₂X groups per 10⁶ carbon atomsand up to 100 unstable end groups per 10⁶ carbon atoms, wherein X isindependently —F, —NH₂, —OH, or —OZ, wherein Z is independently ametallic cation or a quaternary ammonium cation, wherein the unstableend groups are selected from —COOM, —CH₂OH, —COF, and —CONH₂, wherein Mis independently an alkyl group, a hydrogen atom, a metallic cation, ora quaternary ammonium cation.

In a second embodiment, the present disclosure provides the copolymer ofthe first embodiment, wherein m is 0.

In a third embodiment, the present disclosure provides the copolymer ofthe first or second embodiment, wherein z is 1 or 2.

In a fourth embodiment, the present disclosure provides the copolymer ofany one of the first to third embodiments, wherein Rf is —CF₃, andwherein n is 1 or 3.

In a fifth embodiment, the present disclosure provides the copolymer ofthe first or second embodiment, wherein m is 0, and z is 0.

In a sixth embodiment, the present disclosure provides the copolymer ofany one of the first to fifth embodiments having not more than 50unstable end groups per 10⁶ carbon atoms.

In a seventh embodiment, the present disclosure provides the copolymerof any one of the first to sixth embodiments having not more than 25unstable end groups per 10⁶ carbon atoms.

In an eighth embodiment, the present disclosure provides the copolymerof any one of the first to seventh embodiments having at least 10 —SO₂Xgroups per 10⁶ carbon atoms.

In a ninth embodiment, the present disclosure provides the copolymer ofany one of the first to eighth embodiments having at least 25 or atleast 50 —SO₂X groups per 10⁶ carbon atoms.

In a tenth embodiment, the present disclosure provides the copolymer ofany one of the first to ninth embodiments, wherein the copolymercomprises less than 50 ppm alkali-metal cations.

In an eleventh embodiment, the present disclosure provides the copolymerof any one of the first to ninth embodiments, wherein the copolymercomprises at least 50 ppm alkali-metal cations.

In a twelfth embodiment, the present disclosure provides the copolymerof any one of the first to eleventh embodiments, wherein the copolymerhas a polydispersity of less than or equal to 2.5.

In a thirteenth embodiment, the present disclosure provides thecopolymer of any one of the first to twelfth embodiments, furthercomprising units derived from at least one perfluorinated terminalolefin independently having from 3 to 8 carbon atoms.

In a fourteenth embodiment, the present disclosure provides thecopolymer of the thirteenth embodiment, wherein the units derived fromat least one perfluorinated terminal olefin are hexafluoropropyleneunits.

In a fifteenth embodiment, the present disclosure provides the copolymerof the fourteenth embodiment, wherein the hexafluoropropylene units arepresent in the copolymer at 10 percent to 17 percent by weight, based onthe total weight of the copolymer.

In a sixteenth embodiment, the present disclosure provides the copolymerof any one of the first to the fifteenth embodiments having a meltingpoint in a range from 220° C. to 285° C.

In a seventeenth embodiment, the present disclosure provides thecopolymer of any one of the first to sixteenth embodiments, wherein thecopolymer is not foamed.

In an eighteenth embodiment, the present disclosure provides thecopolymer of any one of the first to sixteenth embodiments, wherein thecopolymer is foamed.

In a nineteenth embodiment, the present disclosure provides thecopolymer of any one of the first to eighteenth embodiments, wherein thecopolymer has a melt flow index (measured at 372° C./5 kg) in a rangefrom 25 grams per 10 minutes to 35 grams per 10 minutes.

In a twentieth embodiment, the present disclosure provides the copolymerof any one of the first to nineteenth embodiments, wherein the SO₂Xgroups comprise SO₂X end groups.

In a twenty-first embodiments, the present disclosure provides thecopolymer of any one of the first to twentieth embodiments, wherein thecopolymer further comprises units represented by formula

wherein a is 0 or 1, each b is independently from 1 to 4, c is 0 to 4, dis 0 or 1, e is 1 to 6, and X is independently —F, —NH₂, —OH, or —OZ,and wherein Z is independently a metallic cation or a quaternaryammonium cation.

In a twenty-second embodiment, the present disclosure provides thecopolymer of the twenty-first embodiment, wherein c is 0, d is 1, and eis 1 to 4.

In a twenty-third embodiment, the present disclosure provides thecopolymer of the twenty-first embodiment, wherein a is 0, OC_(b)F_(2b)is OCF₂CF(CF₃), c is 1 or 2, d is 1, and e is 1 to 4.

In a twenty-fourth embodiment, the present disclosure provides thecopolymer of the twenty-first embodiment, wherein a is 1, b is 1, c is 0to 4, d is 1, e is 1 to 4.

In a twenty-fifth embodiment, the present disclosure provides a methodof making an extruded article, the method comprising extruding a meltedcomposition comprising (or consisting of) the copolymer of any one ofthe first to twenty-fourth embodiments.

In a twenty-sixth embodiment, the present disclosure provides the methodof the twenty-fifth embodiment, wherein the extruded article comprisesat least one of a film, tube, pipe, or hose.

In a twenty-seventh embodiment, the present disclosure provides themethod of the twenty-fifth or twenty-sixth embodiment, wherein themelted composition is extruded onto a conductor.

In a twenty-eighth embodiment, the present disclosure provides themethod of any one of the twenty-fifth to twenty-seventh embodiments,wherein the melted composition is extruded onto a cable or wire.

In a twenty-ninth embodiment, the present disclosure provides anextruded article comprising the copolymer of any one of the first totwenty-fourth embodiments.

In a thirtieth embodiment, the present disclosure provides the extrudedarticle of the twenty-ninth embodiment, wherein the extruded articlecomprises at least one of a film, tube, pipe, or hose.

In a thirty-first embodiment, the present disclosure provides theextruded article of the twenty-ninth or thirtieth embodiment, whereinthe extruded article is a conductor having the copolymer extrudedthereon.

In a thirty-second embodiment, the present disclosure provides theextruded article of any one of the twenty-ninth to thirty-firstembodiments, wherein the extruded article is a cable or wire having thecopolymer extruded thereon.

In a thirty-third embodiment, the present disclosure provides the methodof any one of the twenty-fifth to twenty-eighth embodiments or theextruded article of any one of the twenty-ninth to thirty-secondembodiments, wherein the extruded article is not foamed.

In a thirty-fourth embodiment, the present disclosure provides themethod of any one of the twenty-fifth to twenty-eighth embodiments orthe extruded article of any one of the twenty-ninth to thirty-secondembodiments, wherein the extruded article is foamed.

In a thirty-fifth embodiment, the present disclosure provides a methodof making the copolymer of any one of the first to nineteenthembodiments, the method comprising copolymerizing components comprisingtetrafluoroethylene and at least one compound independently representedby formula CF₂═CF(CF₂)_(m)(OC_(n)F_(2b))_(z)ORf, wherein each n isindependently from 1 to 6, m is 0 or 1, z is 0, 1, or 2, and Rf is alinear or branched perfluoroalkyl group having from 1 to 8 carbon atomsand optionally interrupted by one or more —O— groups.

In a thirty-sixth embodiment, the present disclosure provides the methodof the thirty-fifth embodiment, wherein copolymerizing is carried out byaqueous emulsion polymerization.

In a thirty-seventh embodiment, the present disclosure provides themethod of the thirty-fifth embodiment, wherein copolymerizing is carriedout by suspension polymerization.

In a thirty-eighth embodiment, the present disclosure provides themethod of any one of the thirty-fifth to thirty-seventh embodiments,wherein the components further comprise at least one perfluorinatedterminal olefin independently having from 3 to 8 carbon atoms.

In a thirty-ninth embodiment, the present disclosure provides the methodof any one of the thirty-fifth to thirty-eighth embodiments, wherein thecomponents further comprise at least one compound represented by formulaCF₂═CF(CF₂)_(a)—(OC_(b)F_(2b))_(c)—(O)_(d)—(C_(e)F_(2e))—SO₂X, wherein ais 0 or 1, each b is independently from 1 to 4, c is 0 to 4, d is 0 or1, e is 1 to 6, wherein X is independently —F, —NH₂, —OH, or —OZ, andwherein Z is independently a metallic cation or a quaternary ammoniumcation.

In a fortieth embodiment, the present disclosure provides the copolymerof the thirty-ninth embodiment, wherein c is 0, d is 1, and e is 1 to 4.

In a forty-first embodiment, the present disclosure provides thecopolymer of the thirty-ninth embodiment, wherein a is 0, OC_(b)F_(2b)is OCF₂CF(CF₃), c is 1 or 2, d is 1, and e is 1 to 4.

In a forty-second embodiment, the present disclosure provides thecopolymer of the thirty-ninth embodiment, wherein a is 1, b is 1, c is 0to 4, d is 1, e is 1 to 4.

In a forty-third embodiment, the present disclosure provides the methodof any one of the thirty-fifth to forty-second embodiments, whereincopolymerizing is carried out in the presence of a bisulfate or sulfitesalt.

In order that this disclosure can be more fully understood, thefollowing examples are set forth. It should be understood that theseexamples are for illustrative purposes only and are not to be construedas limiting this disclosure in any manner. Abbreviations include g forgrams, kg for kilograms, m for mass, mm for millimeters, L for liters,min for minutes, hrs for hours, rpm for revolutions per minute.

EXAMPLES

Test Methods:

MFI

The melt flow index (MFI), reported in g/10 min, was measured with aGoettfert MPX 62.92 melt indexer (Buchen, Germany) following a similarprocedure to that described in DIN EN ISO 1133-1:2012-03 at a supportweight of 5.0 kg and a temperature of 372° C. The MFI was obtained witha standardized extrusion die of 2.1 mm in diameter and a length of 8.0mm.

Melting Point

The melting point of the fluorothermoplastic polymer was determinedusing differential scanning calorimetry following a similar procedure tothat described in ASTM D4591-07 (2012) using a PerkinElmer Pyris 1 DSC(Waltham, Mass., USA) under nitrogen flow with a heating rate of 10°C./min. The reported melting points relate to the melting peak maximum.

Particle Size

The latex particle size determination was conducted by means of dynamiclight scattering with a Malvern Zetasizer 1000HSA (Malvern,Worcestershire, UK) following a similar procedure to that described inDIN ISO 13321:2004-10. The reported average particle size is thez-average. Prior to the measurements, the polymer latexes as yieldedfrom the polymerizations were diluted with 0.001 mol/L KCl-solution. Themeasurement temperature was 20° C. in all cases.

Monomer Unit Content

The content of CF₂═CF—CF₂—O—(CF₂)₃—OCF₃ (MA-31), CF₂═CF—CF₂—O—C₃F₇(MA-3), CF₂═CF—O—(CF₂)₃—OCF₃ (MV-31), CF₂═CF—O—C₃F₇ (PPVE-1),CF₂═CF—O—CF₂—CF(CF₂)—O—CF₂—CF₂—SO₂F (PSEPVE), and CF₂═CF—CF₃ (HFP) inthe copolymer was determined by Fourier-transform infrared spectroscopy.Thin films of approximately 0.1 mm thickness were prepared by moldingthe polymer at 350° C. using a heated plate press. The films were thanscanned in nitrogen atmosphere using a Nicolet DX 510 FT-IRspectrometer. The OMNIC software (ThermoFisher Scientific, Waltham,Mass./USA) was used for data analysis. The content of MA-31, MA-3,MV-31, PPVE-1, PSEPVE and HFP, reported in units of m/m %, wasdetermined from an IR band at a monomer-specific wavenumber ν_(M) andwas calculated as a product of a monomer-specific factor ε_(rel) and theratio of the absorbance of the IR-peak at ν_(M), A(ν_(M)), to theabsorbance of the IR-peak at 2365 cm⁻¹, A(2365 cm⁻¹), meaningε_(rel)×A(ν_(M))/A(2365 cm⁻¹). Wavenumbers ν_(M) and factors ε_(rel) aregiven in the following table:

wave- number ν_(M) factor monomer [1/cm] ε_(rel)CF₂═CF—CF₂—O—(CF₂)₃—OCF₃ 892 3.81 CF₂═CF—CF₂—O—C₃F₇ 995 61CF₂═CF—O—(CF₂)₃—OCF₃ 893 3.24 CF₂═CF—O—C₃F₇ 993 0.95CF₂═CF—O—CF₂—CF(CF₃)—O—CF₂—CF₂—SO₂F 1467 1.06 CF₂═CF—CF₃ 983 3.2

In case of the simultaneous presence of PPVE-1 and HFP, thedeconvolution software “Peak Fit” from AISN Software Inc., version 4.06,was used to determine the monomer-specific absorbance of the IR-peak atν_(M). The automatic peak detection and fitting method II, secondderivative method, was applied.

End Group Analysis

Polymer end group detection was conducted in analogy to the methoddescribed in U.S. Pat. No. 4,743,658 (Imbalzano et al.). Thin films ofapproximately 0.50 mm were scanned on the same Nicolet Model 510Fourier-transform infrared spectrometer. 16 scans were collected beforethe transform is performed, all other operational settings used werethose provided as default settings in the Nicolet control software.Similarly, a film of a reference material known to have none of the endgroups to be analyzed was molded and scanned. The reference absorbancespectrum is subtracted from the sample absorbance, using the interactivesubtraction mode of the software. The CF₂ overtone band at 2365wavenumbers is used to compensate for thickness differences betweensample and reference during the interactive subtraction. The differencespectrum represents the absorbances due to non-perfluorinated polymerend groups. The number of end groups per million carbon atoms wasdetermined via the equation: ends/1e6 carbons=absorbance×CF/filmthickness in mm. The calibration factors (CF) used to calculate thenumbers of end groups per million carbon atoms are summarized in thefollowing table:

Calibration End group Wavenumber [1/cm] Factor (CF) —COF 1885 1020—CONH₂ 3438 1105 —COOH, isolated 1814 740 —COOH, associated 1775 112—CF₂H 2950-3050 (integrated) 846 —CF(CF₃)H 2820-3000 (integrated) 224—CF═CF₂ 1784 532 —SO₂F 1467 400 —SO₃H 1063 3030After the interactive subtraction, the absorbance of the —SO₃H peak wasnot quantified using the OMNIC software of the Nicolet Model 510Fourier-transform infrared spectrometer, because the weak —SO₃H peak ispartially overlapping by other peaks in the direct neighborhood of 1063l/cm and it appears as part of a peak-shoulder around 1050 l/cm. In thiscase, the deconvolution software “Peak Fit” from AISN Software Inc.,version 4.06, was used to determine the absorbance the —SO₃H peak. Theautomatic peak detection and fitting method II, second derivativemethod, was applied with usually about 22% smoothing to a wavenumberregion of 1020 to 1075 l/cm. Four Pearson VII Amplitude peaks of uniformwidth and a linear 2 point baseline were usually applied to fit thatregion. The —SO₃H peak is the one located at the highest wavenumber, thecorresponding absorbance is the parameter a0 taken from peak fitsummary.

The —CF₂H peak is discernible at a peak around 3009 l/cm with a shoulderat about 2983 l/cm. The peak deconvolution procedure “Peak Fit” softwarefrom AISN Software Inc applied as described above in a region in between2900 and 3100 l/cm reveals additional peaks located at about 2936, 2960,3032 and 3059 l/cm. These peaks are integrated and the number of endgroups per million carbon atoms was determined from the total peak areavia the equation: ends/1e6 carbons=area×CF/film thickness in mm, whereina Calibration Factor of 846 was applied.

The —CF(CF₃)H group shows a broad peak band with main peaks around 2973,2930 and 2858 l/cm. The peak deconvolution procedure “Peak Fit” softwarefrom AISN Software Inc applied in a region in between 2820 and 3000 l/cmmay reveal additional peaks located at about 2830, 2845, 2871, 2885,2900, 2916, 2943 and 2258 l/cm. These peaks are integrated and thenumber of end groups per million carbon atoms was determined from thetotal peak area via the equation: ends/1e6 carbons=area×CF/filmthickness in mm, wherein a Calibration Factor of 224 was applied. When—CF₂H groups and CF(CF₃)H groups are present at one time, the peakdeconvolution procedure needs to be applied to the wavenumber region inbetween 2820 and 3050 l/cm. Then, the contributions of both groups tothe broad peak need to be separated from each other and consideredindependently using the equations given above.

Polydispersity Determination by Melt Rheology

Oscillatory shear flow measurements were conducted on fluoropolymermelts using a strain controlled ARES rheometer (3ARES-13; Firmwareversion 4.04.00) (TA Instruments Inc., New Castle, Del., USA) equippedwith a FRT 200 transducer with a force range of up to 200 g. Dynamicmechanical data were recorded in nitrogen atmosphere in frequency sweepexperiments using a 25 mm parallel plate geometry and a plate to platedistance of usually 1.8 mm was realized. Individual frequency sweepswere recorded at a temperature of 372° C., 340° C., 300° C., 280° C. andin super-cooled melt at 260° C. The thermal control of the oven wasoperated using the sample/tool thermal element. A strain typicallyascending from 1 to 20% was applied while the shear rate was descendedfrom 100 rad/s to typically 0.1 rad/s. Using thetime-temperature-superposition (TTS) tool provided by the orchestratorsoftware (version 7.0.8.13), these individual frequency sweeps werecombined to one master curve, wherein T=372° C. was selected as thereference temperature. Zero shear viscosities η₀, reported in units ofPa×s, were extrapolated from the viscosity function η*(ω) of theobtained dynamic mechanical master curve using the 4 parameter Carreaufit function provided by the orchestrator software. The molecular weightdistribution of fluoropolymer melts were extracted from the so-obtaineddynamic mechanical data by the procedure disclosed by W. H. Tuminello inPolym. Engineering Sci., 26, 1339-1347 (1986) and in Encyclopedia ofFluid Mechanics, Vol. 9, Polymer Flow Engineering, 209. The methodincludes that the frequency is converted into a molecular weight. In thepresent case, the equation1/ω=7.63e-22×M ^(3.6)was used. In the same way as described by Tuminello, the cumulativemolecular weight distribution (CMWD) is evaluated by forming theexpressionCMWD=100×{1−[G′(ω)/G _(N) ⁰]^(0.5)}.Herein, a plateau modulus of G_(N) ⁰=1.1e6 Pa was used. In modificationof the method described by Tuminello, the sigmoidal CMWD is approximatedby a function of the Weibull-type:CMWD=100*(1−exp(−((x+d*(b−x0))/b){circumflex over ( )}c)), with x=log M,

d=((c−1)/c){circumflex over ( )}(1/c); c=3.376+2.305*b;b=1.8+9.154e-4*600.95{circumflex over ( )}chi

A user defined fit routine operating under the software SigmaPlot 12.5(Systat Software, Inc.; San Jose/CA, USA) was used to determine the twofit parameters x0 and chi. The first derivative of the fit function wasevaluated by applying the macro “Compute 1^(st) Derivative” provided bythe SigmaPlot 12.5 software. The first derivative of the fit function isrepresenting a Schulz-Zimm distribution described by Equation (6) inAuhl et al., Macromolecules 2006, Vol. 39, No. 6, p. 2316-2324. Themaximum of this distribution is given by the number average molecularweight M_(N) and its breadth is controlled by the degree of coupling k.The degree of coupling k is then converted into the polydispersity indexM_(W)/M_(N) according to a 5-order polynomial:k=d0+d1×U+d2 {circumflex over ( )}U{circumflex over( )}2+d3×U{circumflex over ( )}3+d4×U{circumflex over( )}4+d5×U{circumflex over ( )}5; with U=M _(W) /M _(N)

d0=183.3296154186 d1=−445.7760158725

d2=443.8169326941 d3=−223.4535380971

d4=56.6264675389 d5=−5.7637913869

Finally, the consistency of the obtained result is probed by comparingthe mass average molecular weight M_(W) of this Schulz-Zimm distributionwith the one obtained from the zero shear viscosity by:η₀(372° C.)=9.36e-17×M _(W) ^(3.6)The molecular weight distribution is correctly extracted from therheology data in the case that both Mw values deviate from each other byless than ±5%. The results reported herein fulfill this consistencycriterion.Alkali-Ion Content

For the determination of the alkali-ion content, 1 g polymer wascombusted in a muffle-type furnace (Linn High Term; Eschenfelden,Germany; VMK39μP) for 10 hrs (air at 550° C.). The incineration residuewas dissolved into 50 mL of a 4 vol. % aqueous solution of HCl/HF (5:1)(HCl: 30% aqueous solution available from Merck, Darmstadt/Germany,under the trade designation “SUPRAPUR”; HF: 40% aqueous solutionavailable from Merck, Darmstadt/Germany under the trade designation“SUPRAPUR”). The acidic solution was further analyzed by an “AANALYST200” Perkin Elmer flame atomic absorption spectrometer (Waltham,Mass./USA). The instrument was calibrated with 0.500 ppm and 1.000 ppmpotassium aqueous standard solutions (Merck; Darmstadt/Germany;“CERTIPUR” Element Standard Solution). The peak height at a wavelengthof 766.5 nm was used to evaluate the potassium content. The peak heightat a wavelength of 589 nm was used to evaluate the sodium content.

Peel Strength

The peel strength of copper-polymer interfaces was determined using aZwick materials testing machine Z010 with the software TestExpert 2(Ulm, Germany). A 0.05 mm thick copper foil (O.F.H.C, 99.95%, half hard;Sigma-Aldrich, St. Louis, Mo., USA) was cleaned by storing it for 30 minat ambient temperature in an 1.5 wt. % aqueous solution of sulfamic acid(98%, Sigma-Aldrich), subsequent rinsing with purified water, and dryingwith a paper towel. Copper foil and polymer were pressed in between two50 μm thick Kapton® 200 HN foils (Krempel, Vaihingen an der Enz,Germany) for 5 min at 360° C. and 53 bar to generate a 0.8 mm thickcopper-polymer plate. Part of the copper foil was separated from thepolymer during heat-pressing by a Kapton® foil to avoid bonding in thispart. After conditioning for 20 hours at ambient pressure and 23° C. aswell as removal of the Kapton® foils, 15 mm wide test specimens werepunched out by means of a DIN 53455-08.1981 type punching knife (fortest specimen no. 5; NAEF, Adliswil, Switzerland). The unbonded copperend was bent by 180° and then both unbonded ends were clamped in thetest grips of the materials testing machine. The load was applied at 23°C. at a constant head speed of 150 mm/min and the load versus headmovement was recorded while separating both materials at an angle ofapproximately 180°. The average peeling load for the first 30 mm ofpeeling after the initial peak was determined in Newton. The peelstrength data reported herein refer to an average of at least fourindividual test runs.

Example 1

CF₂═CF—O—C₃F₇ (PPVE-1) was prepared from HFPO using well-known syntheticmethods.

A polymer of Tetrafluoroethylene (TFE), Hexafluoropropylene (HFP) andCF₂═CF—O—C₃F₇ (PPVE-1) was prepared:

A 52-L-polymerization kettle with an impeller agitator was charged with29 L deionized water, 48 g aqueous 30 wt. % ammonia-solution and 440 gof a 30 wt. % aqueous solution of ammonium4,8-dioxa-3-H-perfluorononanoate (CF₃—O—(CF₂)₃—O—CFH—CF₂—COONH₄,prepared as described in “Preparation of Compound 11” in U.S. Pat. No.7,671,112). The oxygen-free kettle was than heated to 70° C., theagitation system was set to 240 rpm, and 30 g Na₂S₂O₅ were added. PPVE-1(40 g) was added, and TFE/HFP at a ratio of 40.7/59.3 mol % were addeduntil a final pressure of 17.0 bar (1700 kPa) was reached. Thepolymerization was initiated by adding 5 g ammonium peroxydisulfate(APS), dissolved in 100 mL H₂O. The polymerization temperature wasmaintained at 70° C., and the pressure was kept at 17 bar (1700 kPa).The monomers feed was constant; overall 5.0 kg TFE, 0.45 kg HFP and 65 gPPVE-1 were fed. A solution of 50 g APS in 500 mL H₂O was also fed afterpolymerization has started; feeding of APS was continued until 95% ofthe total monomers were consumed. The total runtime was 2 hours 28minutes. The obtained latex had a solid content of 15.6 wt %, theaverage particle size was 59 nm. The latex was coagulated by theaddition of aqueous 20 wt. % HCl, agglomerated with gasoline, washedwith deionized H₂O and dried for 16 hours at 190° C. to provide thepolymer. The MFI (372° C./5 kg) was 35 g/10 min; the melting point was247° C. The PPVE-1-content was determined as 1.2 wt %, and theHFP-content was determined as 10.8 wt % using the method describedabove. The polydispersity Mw/Mn was 1.73 and the ion contents were Na<5ppm and K<5 ppm.

The endgroups per 10⁶ carbon atoms were determined: COOH, assoc.=138;COOH, iso.=425; 503H=165, and the peel strength of this polymer was 2 N.

Example 2

Post-Fluorination of the Dried Polymer of Example 1:

A 10-L-postfluorination reactor was charged with 100 g of the driedpolymer of Example 1. The oxygen-free reactor was then heated up to 200°C. Then the reactor was evacuated to 0.250 bar absolute (25 kPa). Thevacuum was broken up to a pressure of 0.99 bar absolute (99 kPa) with awith a fluorine gas/nitrogen gas mixture (10 vol. %/90 vol. %, N50, AirLiquide; München/Germany). After 30 minutes reaction time, thefluorine/nitrogen mixture was evacuated to a pressure of 0.250 barabsolute (25 kPa). This process was repeated 4 times. Afterwards thereactor was vented and flushed with N₂ in thirty cycles.

The end groups per 10⁶ carbon atoms were determined: COOH, assoc.=5;COOH, iso.=15; COF=105; SO₃H=94; SO₂F=4.

Example 3

Post-Fluorination of the Dried Polymer of Example 1:

A 10-L-postfluorination reactor was charged with 100 g of the driedpolymer of Example 1. The oxygen-free reactor was then heated up to 200°C. Then the reactor was evacuated to 0.250 bar absolute (25 kPa). Thevacuum was broken up to a pressure of 0.99 bar absolute (99 kPa) with afluorine gas/nitrogen gas mixture (10 vol. %/90 vol. %, N50, AirLiquide; München/Germany). After 30 minutes reaction time, thefluorine/nitrogen mixture was evacuated to a pressure of 0.250 barabsolute (25 kPa). This process was repeated 14 times. Afterwards thereactor was vented and flushed with N₂ in thirty cycles.

The end groups per 10⁶ carbon atoms were determined: COOH, assoc.=4;COOH, iso.=2; SO₃H=24; SO₂F=7, and the peel strength of this polymer was0.95 N.

Comparative Example 1

3M™ Dyneon™ FEP6322Z, commercially available from 3M Company, St. Paul,Minn., USA, with an MFI (372° C./5 kg) of 25 g/10 min waspost-fluorinated for 14 cycles/30 min each at 200° C.; the end groupsper 10⁶ carbon atoms were determined: COOH, assoc.=2; COOH, iso.=0;COF=1 and the peel strength of this polymer was 0.57 N.

Various modifications and alterations of this disclosure may be made bythose skilled in the art without departing from the scope and spirit ofthe disclosure, and it should be understood that this invention is notto be unduly limited to the illustrative embodiments set forth herein.

What is claimed is:
 1. A copolymer comprising tetrafluoroethylene units,units independently represented by formula

in a range from 0.02 to 2 mole percent, based on the total amount of thecopolymer, wherein each n is independently from 1 to 6, m is 0 or 1, zis 0, 1, or 2, and Rf is a linear or branched perfluoroalkyl grouphaving from 1 to 8 carbon atoms and optionally interrupted by one ormore —O— groups, and units represented by formula

wherein a is 0 or 1, each b is independently from 1 to 4, c is 0 to 4, dis 0 or 1, e is 1 to 6, and X is independently F, —NH₂, —OH, or —OZ, andwherein Z is independently a metallic cation or a quaternary ammoniumcation, wherein the copolymer has a melt flow index in a range from 20grams per 10 minutes to 40 grams per 10 minutes measured at atemperature of 372° C. and at a support weight of 5.0 kg, and whereinthe copolymer has in a range from 2 to 200 SO₂X groups per 10⁶ carbonatoms and up to 100 unstable end groups per 10⁶ carbon atoms, wherein Xis independently —F, —NH₂, —OH, or —OZ, wherein Z is independently ametallic cation or a quaternary ammonium cation, wherein the unstableend groups are selected from —COOM, —CH₂OH, —COF, and —CONH₂, andwherein M is independently an alkyl group, a hydrogen atom, a metalliccation, or a quaternary ammonium cation.
 2. The copolymer of claim 1,wherein m is
 0. 3. The copolymer of claim 1, wherein Rf is —CF₃, andwherein n is 1 or
 3. 4. The copolymer of claim 1, wherein z is 1 or 2.5. The copolymer of claim 1, wherein the copolymer has a polydispersityof less than or equal to 2.5.
 6. The copolymer of claim 1, wherein c is0, d is 1, and e is 1 to 4; or wherein a is 1, b is 1, c is 0 to 4, d is1, e is 1 to
 4. 7. A method of making an extruded article, the methodcomprising extruding a melted composition comprising the copolymer ofclaim
 1. 8. An extruded article comprising the copolymer of claim
 1. 9.The extruded article of claim 8, wherein the extruded article comprisesat least one of a film, tube, pipe, or hose.
 10. The extruded article ofclaim 8, wherein the extruded article is a conductor having thecopolymer extruded thereon.
 11. The extruded article of claim 8, whereinthe extruded article is a cable or wire having the copolymer extrudedthereon.
 12. A method of making the copolymer of claim 1, the methodcomprising copolymerizing components comprising tetrafluoroethylene andat least one compound independently represented by formulaCF₂═CF(CF₂)_(m)(OC_(n)F_(2n))_(z)ORf, wherein each n is independentlyfrom 1 to 6, m is 0 or 1, z is 0, 1, or 2, and Rf is a linear orbranched perfluoroalkyl group having from 1 to 8 carbon atoms andoptionally interrupted by one or more —O— groups.
 13. The method ofclaim 12, wherein copolymerizing is carried out in the presence of abisulfite or sulfite salt.
 14. The copolymer of claim 1, wherein a is 0,OC_(b)F_(2b) is OCF₂CF(CF₃), c is 1 or 2, d is 1, and e is 1 to
 4. 15. Acopolymer comprising tetrafluoroethylene units and units independentlyrepresented by formula

in a range from 0.02 to 2 mole percent, based on the total amount of thecopolymer, wherein each n is independently from 1 to 6, m is 0 or 1, zis 0, 1, or 2, and Rf is a linear or branched perfluoroalkyl grouphaving from 1 to 8 carbon atoms and optionally interrupted by one ormore —O— groups, wherein the copolymer has a melt flow index in a rangefrom 20 grams per 10 minutes to 40 grams per 10 minutes measured at atemperature of 372° C. and at a support weight of 5.0 kg, and whereinthe copolymer has in a range from 2 to 200 —SO₂X end groups per 10⁶carbon atoms and up to 100 unstable end groups per 10⁶ carbon atoms,wherein X is independently —F, —NH₂, —OH, or —OZ, wherein Z isindependently a metallic cation or a quaternary ammonium cation, whereinthe unstable end groups are selected from —COOM, —CH₂OH, —COF, and—CONH₂, and wherein M is independently an alkyl group, a hydrogen atom,a metallic cation, or a quaternary ammonium cation.
 16. The copolymer ofclaim 15, further comprising units derived from at least oneperfluorinated terminal olefin independently having from 3 to 8 carbonatoms.
 17. The copolymer of claim 16, wherein the units derived from theat least one perfluorinated terminal olefin are hexafluoropropyleneunits.
 18. The copolymer of claim 17, wherein the hexafluoropropyleneunits are present in the copolymer at 10 percent to 17 percent byweight, based on the total weight of the copolymer.
 19. The copolymer ofclaim 17, wherein the copolymer has a melting point in a range from 220°C. to 285° C.
 20. The copolymer of claim 15, wherein the copolymerfurther comprises units represented by formula

wherein a is 0 or 1, each b is independently from 1 to 4, c is 0 to 4, dis 0 or 1, e is 1 to 6, and X is independently —F, —NH₂, —OH, or —OZ,and wherein Z is independently a metallic cation or a quaternaryammonium cation.